Given That CO₂ Is Produced by Cellular Respiration, Why Does

Given that CO₂ is produced by cellular respiration, why does the amount of CO₂ in the atmosphere remain relatively constant? (When answering this question, exclude the impact of human activities on atmospheric CO₂.)

A) CO₂ is converted in photosynthesis to carbohydrates.
B) CO₂ is split apart during photosynthesis.
C) CO₂ mostly forms carbonate rocks.
D) CO₂ is trapped in dead organisms' bodies.